1. Field of the Invention
The present invention relates to a method for producing an exhaust pipe.
2. Discussion of the Background
In order to treat injurious substances such as injurious gases contained in an exhaust gas discharged from an engine, a catalyst converter is installed in an exhaust gas passage including an exhaust pipe.
In order to improve a purifying efficiency for injurious substances by the catalyst converter, it is necessary to maintain the temperature of an exhaust gas and the temperature of the exhaust pipe and the like through which the exhaust gas is allowed to flow at temperatures suitable for activating the catalyst (hereinafter, referred to also as a catalyst activating temperature).
However, at the time of high-rate driving of the engine, the exhaust gas temporarily has such a high temperature as to exceed 1000° C. Therefore, the temperature of the exhaust gas sometimes becomes higher than the upper limit value of the catalyst activating temperature. As a result, problems are raised in that it becomes difficult to efficiently purify an exhaust gas and in that the catalyst deteriorates.
For this reason, an exhaust pipe to be connected to an automobile engine needs to be capable of externally radiating heat of the exhaust gas that flows through the exhaust pipe at the time of high-rate driving of the automobile engine.
JP 2009-133213 A and JP 2009-133214 A have disclosed an exhaust pipe having a structure in which a layer composed of a crystalline inorganic material and an amorphous inorganic material is formed on a surface of a cylindrical base material made of metal.
JP 2009-133213 A has disclosed an exhaust pipe having a structure in which the layer composed of a crystalline inorganic material and an amorphous inorganic material has infrared-ray emissivity higher than the infrared-ray emissivity of the base material so that it is superior in heat releasing characteristic.
Moreover, JP 2009-133214 A has disclosed an exhaust pipe having a structure in which the amorphous inorganic material located on the outer circumferential side from the crystalline inorganic material has an average thickness of 20 μm or less so that it is superior in heat releasing characteristic.
The contents of JP-A 2009-133213 and JP-A 2009-133214 are incorporated herein by reference in their entirety.